i think my msn just got hacked?

hi guys i will try and explain this best i can, basically my old msn account that i let my gf use logged in today (despite my gf sitting next to me watching tv) and started saying some rude stuff to her sister, after talking to the person i decided to sign into the account, i already knew the password so i logged in and it said "msn is sharing connection with (my name)PC and gordonPC (i have no idea who gordon is), they kept signing back in and logging me out but i did manage to delete all contacts, change password and actually delete the whole account is this enough?, this is the first time anything like this has happened to me and hope my pc has not been hacked or anything, does anybody know anything about this? how do i stop this happening in future?